b)No, because their highest valued option forgone may not be the same(eg. they have different job)
c)No, as their monthly salary is the same($30000), but their non-monetary return of this job may not be the same. In other words, their full cost of quitting this job not necessarily be the same.
更新1:
4a)It is the highest valued option forgone b)It is the best alternative use of this amount of money. For example, government can use this amount of money to built infrastructure. The government can also use it to employ more officals.
